The present invention relates to computer telephony systems. More specifically, the invention relates to enhancing the sound quality of computer telephony systems by removing noise.
Conventional telephones operate using circuit-switched technology. The circuit-switched telephone backbone is composed of dedicated copper wires or fiber optic cables that are typically owned by the telephone companies. In general, the telephone companies charge fees for telephone calls based on the duration of the call and the distance between the caller and receiver, which is designed to cover the costs for installing, expanding and maintaining the telephone backbone.
With packet-switched telephone systems, a speaker's voice (or other data) is broken down and sent over a computer network as multiple packets. Computer telephony can offer significant cost savings because dedicated network connections are replaced by network connections shared among many users, which results in much more efficient use of bandwidth and reduced wiring costs. Additionally, in theory, computer telephony can offer easier administration.
One of the main problems inhibiting the widespread adoption of computer telephony systems is that audio quality levels are generally below those of conventional telephony. For example, a persistent complaint has been that computer telephony has relatively high levels of background noise. Currently, the problem of background noise in computer telephony systems has not been satisfactorily resolved.
A traditional engineering solution to background noise is to use a noise gate. Noise gates have been effective in suppressing background noise in high-end public address systems, in multiple microphone and radio broadcasting, and in hearing aids, which are technology areas that generally command high prices and margins. Since noise gates would be required in every client, the high cost associated with noise gates is a major disadvantage of using them in computer telephony, which may require a vastly lower cost structure (e.g., prices and margins may need to be low to compete with conventional telephony).
Another disadvantage of using noise gates in computer telephony is that a noise gate is typically a single output device, meaning that the noise gate gates a single audio stream. Also, noise gates have thus far been inapplicable for computer telephony due to high costs associated with hardware and hybrid hardware-software solutions. In computer telephony, there are typically three audio streams that need to be noise gated at every client, two maintones and the sidetone, each with potentially different processing requirements. Thus, using so many traditional noise gates would be expensive. A low cost way to noise gate three audio streams with different requirements is desirable.
There are many different kinds of noise scenarios that can be present in computer telephony systems. As examples, noise can be present at virtually all frequencies, noise can be present at low frequencies, noise can be present at high frequencies, noise can be present at power line frequencies and harmonics thereof, and any combination of these. The noise is typically caused by the computer telephony environment which includes the computer telephony hardware and network.
Currently, the solution to many of these noise problems is to install hardware filters to client sound cards and possibly to install additional hardware filters within the gateway. A major disadvantage of this solution is that it is expensive, both in terms of equipment costs and personnel time. Furthermore, the hardware filters are generally always left on, which can result in a degradation of fidelity in non-telephony audio applications. Adding hardware to automatically activate the hardware filters will likely increase the cost even more. Moreover, the hardware filters may not be sufficiently flexible as they may be only designed to filter out a specific type of noise.
It would be beneficial to have innovative techniques for enhancing the sound quality of computer telephony systems by removing noise. Additionally, it would be beneficial if the techniques are low cost and flexible within the computer telephony environment.